HR: 11:05h
AN: A32A-04    [Abstracts]
TI: Diurnal Cycles of Aerosol Optical Properties at Pico Tres Padres, Mexico City: Evidences for Changes in Particle Morphology and Secondary Aerosol Formation
AU: * Mazzoleni, C
EM: claudio@lanl.gov
AF: Los Alamos national Laboratory, MSD436, Los Alamos, NM 87544,
AU: Dubey, M
EM: dubey@lanl.gov
AF: Los Alamos national Laboratory, MSD436, Los Alamos, NM 87544,
AU: Chakrabarty, R
EM: Rajan.Chakrabarty@dri.edu
AF: Division of Atmopheric Sciences Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512,
AU: Moosmuller, H
EM: Hans.Moosmuller@dri.edu
AF: Division of Atmopheric Sciences Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512,
AU: Onasch, T
EM: onasch@aerodyne.com
AF: Aerodyne Research Inc., 45 Manning Road, Billerica, MA 01821-3976,
AU: Zavala, M
EM: miguelz@MIT.EDU
AF: Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307,
AU: Herndon, S
EM: herndon@aerodyne.com
AF: Aerodyne Research Inc., 45 Manning Road, Billerica, MA 01821-3976,
AU: Kolb, C
EM: kolb@aerodyne.com
AF: Aerodyne Research Inc., 45 Manning Road, Billerica, MA 01821-3976,
AB: Aerosol optical properties affect planetary radiative balance and depend on chemical composition, size distribution, and morphology. During the MILAGRO field campaign, we measured aerosol absorption and scattering in Mexico City using the Los Alamos aerosol photoacoustic (LAPA) instrument operating at 781 nm. The LAPA was mounted on-board the Aerodyne Research Inc. mobile laboratory, which hosted a variety of gaseous and aerosol instruments. During the campaign, the laboratory was moved to different sites, capturing spatial and temporal variability. Additionally, we collected ambient aerosols on Nuclepore filters for scanning electron microscopy (SEM) analysis. SEM images of selected filters were taken to study particle morphology. Between March 7th and 19th air was sampled at the top of Pico Tres Padres, a mountain on the north side of Mexico City. Aerosol absorption and scattering followed diurnal patterns related to boundary layer height and solar insulation. We report an analysis of aerosol absorption, scattering, and morphology for three days (9th, 11th and 12th of March 2006). The single scattering albedo (SSA, ratio of scattering to total extinction) showed a drop in the tens-of-minutes-to-hour time frame after the boundary layer grew above the sampling site. Later in the day the SSA rose steadily reaching a maximum in the afternoon. The SEM images showed a variety of aerosol shapes including fractal-like aggregates, spherical particles, and other shapes. The absorption correlated with the CO2 signal and qualitatively with the fraction of fractal-like particles to the total particle count. In the afternoon the SSA qualitatively correlated with a relative increase in spherical particles and total particle count. These observed changes in optical properties and morphology can be explained by the dominant contribution of freshly emitted particles in the morning and by secondary particle formation in the afternoon. SSA hourly averaged values ranged from ~0.63 in the morning to ~0.83 in the afternoon/night, indicating light absorbing aerosols, which have a large impact on radiative forcing.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0360 Radiation: transmission and scattering
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting